1. Field of the Invention
The present invention relates to resin-sealing of small objects such as semiconductor devices, and more particularly for sealing with resin in a predetermined configuration by feeding the resin under pressure into a metal mold cavity having a predetermined inner wall configuration.
2. Description of the Background Art
FIG. 16 is a front sectional view of a resin-sealing apparatus for a semiconductor device as an example of conventional resin-sealing apparatuses. The resin-sealing apparatus of FIG. 16 is a multi-plunger type resin-sealing apparatus fabricated by TOWA CORPORATION.
Semiconductor elements 2 are placed on platelike leadframes 1 and are supported in midair in cavities 5 provided in upper and lower metal molds 3 and 4. The cavities 5 are a space in which the leadframes 1 and semiconductor elements 2 are sealed by molding by injection of molten resin thereinto under pressure and are of a configuration corresponding to the resin configuration required after the molding. The upper metal mold 3 includes gates 6 communicating with the cavities 5 and serving as a path of the molten resin. The lower metal mold 4 includes pots 8 which are apertures for housing therein tablets 7 of resin. The upper metal mold 3 further includes culls 9 which are hollows positioned on the upper surface of the pots 8. The cavities 5 communicate with the pots 8 through the gates 6 and culls 9.
The upper metal mold 3 is fixedly mounted to a fixed upper platen 10, and the lower metal mold 4 is fixedly mounted to a lower metal mold stand 11. The lower metal mold stand 11 is fixedly mounted on a mobile platen 12 vertically movable. Heaters 13, 14 for heating and thermal insulation of the upper and lower metal molds 3, 4 are buffed therein, respectively.
Each plunger 15 includes a plunger head 15a and a plunger rod 15b. The plunger heads 15a fitted in the pots 8 feed the tablets 7 to the cavities 5 under pressure. The plunger heads 15a are coupled to respective one end of the plunger rods 15b. The respective other end of the plunger rods 15b is built in a buffer mechanism 16. The buffer mechanism 16 includes string winding springs 16a, a spring case 16b and a nut holder 16c. The string winding springs 16a contact the plunger rods 15b to apply a compressive force thereto. The spring case 16b prevents the plunger rods 15b from slipping off and houses therein the string winding springs 16a to which the compressive force is applied in cooperation with the nut holder 16c.
The nut holder 16c is provided with a female thread to threadingly engage a ball screw shaft 17 provided with a male thread. The ball screw shaft 17 is rotatably supported by a bearing 18 fixed to the mobile platen 12 and acts against a reactive force generated in the ball screw shaft 17 when the tablets 7 are pressurized. The bearing 18 is fixed by bearing stoppers 19 so as not to come out of the mobile platen 12. A driven pulley 20 is fixedly mounted to the ball screw shaft 17 by tightening a nut 21. The ball screw shaft 17 rotates as the driven pulley 20 rotates. A motor 22 produces a running torque of the driven pulley 20. A running torque of the motor 22, after amplified in a speed-reduction gear 23, is transmitted to a driving pulley 24 to be further transmitted to the driven pulley 20 through a belt 25. The motor 22 and the speed-reduction gear 23 are fixedly mounted on the mobile platen 12 through a motor mounting plate 26.
FIG. 17 is a bottom plan view of the upper metal mold 3. One leadframe 1 is provided for eight semiconductor elements 2. The resin-sealing apparatus comprises four culls 9 for each-leadframe 1. The culls 9 are in one-to-one corresponding relation to the pots 8 and plungers 15. Thus the resin-scaling apparatus is of the multi-plunger type in which the plurality of plungers 15 arc provided for the single leadframe 1 and of a two-cavity/pot type in which two cavities 5 are provided for the single pot.